for...in里的i是字符串
forEach(function(值,index,array){})

arr.reduce(function(累计之后的结果,当前元素,index,arr){},初始值)
<script type="text/javascript">
	var arr=[1,2,3,4,5,11];
var res = arr.reduce(function(a,b,c){
	return c;
})
console.log(res)

</script>例子用reduce实现